Basal membrane uptake in potassium-secreting cells of midgut of tobacco hornworm (Manduca sexta).
Basal membrane voltage (Vb), intracellular K+ activity [(K+)i], and short-circuit current (Isc) were measured in isolated posterior midguts of Manduca sexta wherein Isc is a measured of active secretion of K+ from blood into lumen. When bathed in 32 mM K+ and exposed to 100% O2, average values were Isc = 244 microAmp/cm2, Vb = -33.1 mV, and (K+)i = 88.6 mM. The electrochemical gradient across the basal membrane (d mu) averaged +5.8 mV (a gradient favorable for K+ entry). Exposure to 5% O2 led to a new steady state in which Isc = 71 microAmp/cm2, Vb = -18.7 mV, and (K+)i = 99.4 mM. During hypoxia, d mu averaged -9.9 mV (a gradient unfavorable for K+ entry). When the external bathing solution was 10 mM K+, comparable values were, for 100% O2, Isc = 139 microAmp/cm2, Vb = -56.1 mV, (K+)i = 72.2 mM, and d mu = +3.6 mV, and in 5% O2 the values were Isc = 28.3 microAmp/cm2, Vb = -43.7 mV, (K+)i = 76.1 mM, and d mu = -10.2 mV. The failure of cellular K+ to fall during prolonged hypoxia is evidence for a thermodynamically active basal K+ uptake process.
Chao
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AC
Department of Zoology, Washington State University, Pullman 99164.
Koch
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Moffett
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D000818:Animals; D001464:Barium / Q000494:pharmacology; D004563:Electrochemistry; D007413:Intestinal Mucosa / Q000378:metabolism*; D007422:Intestines / Q000166:cytology; D007814:Larva; D007915:Lepidoptera / Q000378:metabolism*; D008566:Membranes / Q000378:metabolism; D009994:Osmolar Concentration; D010100:Oxygen / Q000494:pharmacology; D011188:Potassium / Q000378:metabolism* / Q000494:pharmacology; D012016:Reference Values; D012996:Solutions
D012996:Solutions; D001464:Barium; D011188:Potassium; D010100:Oxygen